Contact allergy to topical corticosteroids occurs more frequently than previously supposed. Cross-allergic phenomena are common. On the basis of a review of the literature and our own patch test data on 15 patients, we conclude that positive patchtests to corticosteroids occur approximately six to seven times more frequently in well-defined groups of structurally-related substances than between corticosteroids of different groups. An analogous substitution pattern on the steroid D-ring or the carbon side chain (C20, C21) seems to have a significant influence on the association of positive patchtest results. This is not the case for other structural variables, such as the presence of a double bond in the steroid A-ring or fluoride substitutions on the B-ring. The effect of other factors such as concomitant sensitization and steroid metabolism in the skin on the development of a corticosteroid polyallergy are analysed, and the specificity and sensitivity of cross-allergy phenomena are evaluated. These are important in the selection of a topical steroid in the future treatment of a corticosteroid sensitive patient.